While Galileo and other missions, as well as ground-based observations, have taught us much about Io’s frequent and diverse forms of volcanism, the stochastic nature of volcanic outbursts remains a poorly constrained phenomenon. Outbursts have been outliers in many Io observation campaigns since the 1980s (Veeder 1994; Stansberry 1997; Howell, de Kleer 2016), and we present another data-set with which to derive cases and statistics of volcanic outbursts. We define outbursts as a brightness greater than 80 GW/sr/micron above Io’s background brightness, in the L’ filter. Of 120 observations with NASA’s Infrared Telescope Facility (IRFT) 2016-2020, three definitive outbursts were identified on May 10, 2018; May 28, 2019; and June 25, 2019. On May 28 and June 25 of 2019, we observed Io in eclipse and throughout its occultation with the L’ band (3.5 microns). On May 10, 2018, we observed Io in reflected sunlight using the K, L’, and M bands. While the emission includes all of Io, we expect the outburst to dominate at these shorter infrared wavelengths. Fitting a single temperature blackbody to the measured emission suggests that this outburst is composed of localized silicate lava-flows with temperatures greater than 1,100 K over areas less than 30 km2. The locations of these three outbursts are consistent with several known active Ionian volcanoes, although the low spatial resolution does not allow us to determine the exact source. Images from Juno’s instrument are used to constrain the afterglow location for the June 2019 outburst.
Variations in volcanism on Io, particularly large outbursts, are the most plausible explanation for variations in Jupiter’s magnetosphere and aurora. If outbursts are a major source of changes in Jupiter’s magnetosphere and aurorae, our observations suggest such changes would have occurred in mid-2018 and mid-2019.
We also present the time-series of Io’s total eclipse brightness and Loki’s brightness for the duration of this observation campaign. The outburst times do not correlate with Loki’s periodic brightening events or any other pattern discernable in the time-series.